Contoured reamer teeth

ABSTRACT

An acetabular reamer ( 10 ′) for cutting a required cut shape. The reamer has a cutting shell ( 12 ′) having a series of doubly curved cutting teeth ( 16 ′) thereon of a quantity to substantially reduce a cutting pressure on each tooth as well as to reduce a size of a typical chip generated upon cutting. Substantially all the teeth each have a matched arc cutting edge ( 20′ ) of substantial length that has a cutting profile which substantially matches a profile of a shape to be cut. Such a configuration reduces the number of teeth required to cut the shape.

BACKGROUND OF THE INVENTION

The invention relates to surgical products, and in particular, tosurgical reamers for cutting shaped cavities in bone.

In order to produce a shaped cavity in bone for a hip implant, whichrequires smooth walls and accurate shape, it is advantageous that thereamer shell or cutting bowl be hemispherical. Further, the cuttingteeth must be properly located and oriented. Still further, the toothheight is important to the size of bone chip and thus to the accuracy ofthe shape cut by the reamer.

In most cases, an implant in a hip socket is best fixed to a concave,hemispherical cavity. However, such a shape is not strictly necessary.Other acetabular cutting shells are non-hemispherical but the principleexplained here may be adapted to include such other geometries.

It is increasingly important, especially with cementless hip surgery,that the acetabulum be reamed to an exact form, generally a hemisphere,thus allowing maximal contact between the bone and the definitive(hemispherical) implant.

Further, there is increasing emphasis on cutting a smaller incision tominimise the trauma to the patient and to aid the rate of recovery.Meeting this additional requirement provides an additional challenge tothe designers of medical instruments and implants. In addition, thechange in surgical procedure includes the fact that the surgeon now moreoften maintains the acetabular reamer handle on a single axis ratherthan performing the step of “sweeping” the end of the tool handlethrough an angle and thus continuously changing the axis of the reamercut. If a test is made maintaining a prior art reamer handle on aconstant axis, then a series of concentric rings are cut that, on amacro-scale, approximate a hemisphere. When the surgeon “sweeps” theaxis of the reamer handle, these irregularities are removed (in asimilar manner to polishing) yielding a hemispherical surface.

In an effort to maximize the number of concentric rings, to minimizechatter/vibration and thus approach a smooth hemispherical surfacewithout sweeping, it is desirable to add more teeth. However, when thisis done, mechanical strength decreases. Further, it is more difficult inthis case to insure that the cut profile of each tooth overlaps. Largerteeth have been attempted but either the chip size and cutting stresseswere too large or the reamer was too complex. Further, due to the largeopening adjacent the larger teeth, mechanical strength was sacrificed.

U.S. Pat. No. 5,116,165 to Sayler describes a reamer having a limitednumber of discrete blade-like teeth. These teeth are defined by a singlecurve of the profile of the form to be cut. In other words, these teethare flat. Such a tooth form thus is not supported in that no structureis provided to help maintain the form of the tooth (other than the toothitself) when faced with the sometimes unusually high cutting pressuresof reaming. Further, the integrity of the spherical form of the reamercan be affected when there are a limited number of extensive slits ofcuts in the spherical. This integrity is affected by the fact that highstresses are induced at the sharp corners of the slits.

Often the form of the tooth is a function of the original material form:the sheet material or the base diameter of the hemisphere or of themanufacturing method. Often no consideration is given to the form of thecut surface. Therefore, the cut of a single tooth often onlyapproximates the required form of a sphere or a hemisphere. For example,it may yield a planar surface or have a radius different than thatrequired and further generate an overall hemisphere that is irregular.

Therefore, what is needed is a reamer that minimizes the discrete cutsurfaces and generate a series of cuts that comprise a single definedgeometry. Further, what is needed is a tooth form that can be controlledindependently of the form of the original material form.

SUMMARY OF THE INVENTION

The above problems are solved through the provision of an acetabularreamer for cutting a required cut shape, the reamer having a cuttingshell on which are located a series of doubly-curved cutting teeththereon of a quantity to substantially reduce a cutting pressure on eachtooth as well as to reduce a size of a typical chip generated uponcutting. Substantially all the teeth each have a matched arc cuttingedge of substantial length that has a cutting profile whichsubstantially matches a profile of a shape to be cut. Such aconfiguration reduces the number of teeth required to cut the shape.Further, by punching up or forming a larger number of smaller teeth, itis easier to maintain the spherical shape of the reamer.

The invention thus gives an improved quality of cut surface and allowsfewer teeth to be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a reamer of the prior art.

FIG. 2A is a top view of a tooth of a reamer of the prior art.

FIG. 2B is a side cross-sectional view of a tooth of a reamer of theprior art

FIG. 2C is a front view of a tooth of a reamer of the prior art.

FIG. 3A is a top view of a tooth of a reamer of the prior art.

FIG. 3B is a side cross-sectional view of a tooth of a reamer of theprior art.

FIG. 3C is a front view of a tooth of a reamer of the prior art.

FIG. 4 is a side view of the reamer of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a typical acetabular reamer 10 of the prior art isshown. The reamer 10 has a cutting bowl or shell 12 defining a surface14 on which are located teeth 16 adjacent openings 18. A base 20provides a tool-engaging device (not shown).

Referring now to FIG. 2A, a tooth 16 of the reamer 10 is shown. Thetooth 16 has a diverging surface 22 (“rise”, marked Zone A) backing upthe cutting edge 20. Some distance behind the cutting edge 20 (to theleft of the cutting edge in the figure), about where the dashed line 26is located, this surface 30 begins to curve inwardly toward the surfaceof Zone B, and then towards the reamer cutting bowl surface 14. Surfacereflection lines 28 help indicate the form of these surfaces.

Referring now to FIG. 2B, a cross sectional side view of the toothprofile 32 of the prior art reamer 10 is shown. The form of the profile32 of the rise 22 is non-linear as indicated.

Referring to FIG. 2C, the diverging surfaces 22 of Zone A are visiblewhen one examines a front view of the tooth 16 of the prior art reamer10. In other prior art reamers, not shown, corresponding portions of therise 22 are not visible in a front view but are hidden from view, due totheir convergence toward an apex.

These rises 22, respective cutting edges 20, and openings 18 are eitherpositioned on the reamer cutting surface in a spiral arrangement orrandomly. The term “spiral” is meant to include any form in which thecutting teeth 16 are orderly organized in a manner to sweep out theentire shape to be cut A preferred spiral arrangement is an arrangementin which adjacent teeth are uniformly angularly offset from each otherat any adjacent circle of latitude, namely, that adjacent teeth lie ondiffering circles of longitude evenly spaced apart from one another.Further, it is preferred that there be a given overlap between adjacentcutting rings (i.e., the rings swept out by each tooth 16).

These prior art reamers 10 have a crest 38, which generally approximatesa narrow Peak.

Referring now to FIGS. 3A to 3C, the present invention has a cuttingshell 12′ on which are located a series of doubly-curved cutting teeth16′ thereon of a quantity to substantially reduce a cutting pressure oneach tooth as well as to reduce a size of a typical chip generated uponcutting. Substantially all the teeth 16′ each have a matched arc cuttingedge 20′ of substantial length that has a cutting profile whichsubstantially matches a profile of a shape to be cut. The matched arccutting edge 20′ is adjacent secondary cutting edges 21′ supported byadjacent rise portions 29′, characterizable as gusset or buttressportions, which curve back toward the cutting shell 12′ and support thesecondary cutting edges 21′. The overall cutting edges 20′ are thereforedoubly-curved in that at least two distinct curves are required todefine each cutting edge 20′. An opening 18′ precedes the cutting edgesas the reamer 10′ is rotated for cutting. Such a configuration reducesthe number of teeth required to cut the shape. The invention thus givesan improved quality of cut surface and allows fewer teeth 16′ to beemployed.

Although the cutting edge 20′ appears flat in the figure, it actuallyfollows the contour of the surface to be cut, in this case, ahemispherical surface. In this embodiment, the radius R of the cuttingedge 20′ matches the radius of the surface to be cut.

Contrary to conventional wisdom, the new tooth 16′ is not generated bythe manufacture of a larger or wider opening 18 adjacent to the tooth.The opening 18′ is, as in the prior art, substantially round in shape.The tooth 16′ is generated by the manner in which the tooth is deformedand the profile of the eventual shape. In this embodiment, the rise 22′approximates the shape of a rectangular prism intersecting the cuttingbowl at a tangent to the surface of the cutting bowl 12. The teeth 16′have clearly diverging surfaces (in Zone A) which follow the cuttingedge 20′. Note that common reference numerals are used for the same oranalogous features throughout the drawings.

Further, it has been learned that by forming or punching up more smallerteeth, it is easier to maintain ensure that the spherical shape of thereamer is not compromised.

For any given radial from the center of the acetabulum to the periphery,a different part of the sector is cut by a different tooth 16′. Theinvention of a longer tooth 16′ following the rounded opening 18′ andwhich matches more closely the required radius R, means that a reducednumber of teeth are required to cut the full radius. Further, the use ofa series of cutting teeth 16′ on the cutting shell 12′ substantiallyreduces the cutting pressure on each tooth as well as to reduce a sizeof a typical chip generated upon cutting. The ability to use fewer teeth16′ further allows sections 50 (shown in FIG. 5) of the hemisphere to beremoved while maintaining a high quality of cut surface. An example of aacetabular reamer with sections cut away is given in the diagrams of PCIapplications serial numbers PCI/IB01/02675 and PCI/IB01/02676 entitledHOLDER FOR A SURGICAL REAMER and SURGICAL REAMER, respectively, filed on21 Dec. 2001, the contents of which are incorporated herein by referencethereto.

The present invention generates a tooth 16′ with a wider cutting profilethat is therefore easier to overlap with the cut generated by the nexttooth at a different latitudinal elevation on the hemisphere.Additionally the tooth 16′ cuts a sector of the required hemisphere,matching the required radius exactly. The improved tooth allows a fullhemisphere to be cut with fewer teeth.

Preferably, the reamer 10′ includes a series of cutting teeth 16′arranged uniformly and spaced apart on the cutting shell. These teeth16′ may be arranged in a spiral arrangement on the cutting shell 12′.

In an alternate embodiment, best seen in FIG. 4, the cutting shell is aportion of a hemisphere, in this case, in which sections 50 (shown bydashed lines) have been removed in the manufacturing process. In thisembodiment, the length of the cutting edges are selected so as tocompletely cut the shape while being of a number that still ensures goodmechanical strength. The longer cutting edges allows the use of lessteeth while still cutting a good hemispherical form than permissiblewith a cutting shell that has a more complete hemispherical shape.

A tool engaging portion 52 is comprised of two intersecting bars 54 and56, one bar 54 of which optionally having two flats 60 (only one ofwhich is shown) on its outer ends, adjacent their connecting points onthe reamer cutting shell 12′.

Multiple variations and modifications are possible in the embodiments ofthe invention described here. Although certain illustrative embodimentsof the invention have been shown and described here, a wide range ofmodifications, changes, and substitutions is contemplated in theforegoing disclosure. In some instances, some features of the presentinvention may be employed without a corresponding use of the otherfeatures. Accordingly, it is appropriate that the foregoing descriptionbe construed broadly and understood as being given by way ofillustration and example only, the spirit and scope of the inventionbeing limited only by the appended claims.

1. An acetabular reamer for cutting a required cut shape, comprising acutting shell having a series of cutting teeth thereon of a quantity tosubstantially reduce a cutting pressure on each tooth as well as toreduce a size of a typical chip generated upon cutting, whereinsubstantially all the teeth are doubly curved, having a matched arccutting edge of substantial length, the matched arc cutting edge havinga cutting profile which substantially matches a profile of the shape tobe cut, thereby reducing a number of teeth required to cut the shape. 2.The reamer of claim 1 wherein a generally circular hole precedes thecutting edges as the reamer is rotated for cutting.
 3. The reamer ofclaim 1, wherein the series of cutting teeth are arranged uniformly andspaced apart on the cutting shell.
 4. The reamer of claim 1, wherein thecutting teeth are arranged in a spiral arrangement on the cutting shell.5. The reamer of claim 1, wherein the cutting shell is a portion of asphere in which the length of the cutting edges are selected so as tocompletely cut the shape, thereby potentially using less teeth thanpermissible with a cutting shell that has a more complete hemisphericalshape.
 6. The reamer of claim 5, wherein the cutting shell is ahemisphere or portion thereof.
 7. The reamer of claim 2, wherein theseries of cutting teeth are arranged uniformly and spaced apart on thecutting shell.
 8. The reamer of claim 2, wherein the cutting teeth arearranged in a spiral arrangement on the cutting shell.
 9. The reamer ofclaim 3, wherein the cutting teeth are arranged in a spiral arrangementon the cutting shell.
 10. The reamer of claim 2, wherein the cuttingshell is a portion of a sphere in which the length of the cutting edgesare selected so as to completely cut the shape, thereby potentiallyusing less teeth than permissible with a cutting shell that has a morecomplete hemispherical shape.
 11. The reamer of claim 3, wherein thecutting shell is a portion of a sphere in which the length of thecutting edges are selected so as to completely cut the shape, therebypotentially using less teeth than permissible with a cutting shell thathas a more complete hemispherical shape.
 12. The reamer of claim 4,wherein the cutting shell is a portion of a sphere in which the lengthof the cutting edges are selected so as to completely cut the shape,thereby potentially using less teeth than permissible with a cuttingshell that has a more complete hemispherical shape.